The vessels shown in the preceding view have been trimmed away and the left half of the optic chiasm has been removed to reveal the infundibulum of the hypophysis (15) extending downward through the opening in the diaphragm of the sella turcica (3). The recesses of the third ventricle that are closely related to the optic chiasm are indicated at 14 and 16. The tentorium has been cut and reflected to reveal the course of the trochlear nerve as it passes anteriorly around the mesencephalon.